U.S. patent number 6,974,421 [Application Number 10/019,451] was granted by the patent office on 2005-12-13 for handheld audiometric device and method of testing hearing.
This patent grant is currently assigned to Everest Biomedical Instruments Co.. Invention is credited to Eldar Causevic, Elvir Causevic.
United States Patent |
6,974,421 |
Causevic , et al. |
December 13, 2005 |
**Please see images for:
( Certificate of Correction ) ** |
Handheld audiometric device and method of testing hearing
Abstract
Handheld apparatus (100), and method for comprehensive hearing
testing with pass/refer results applicable for large scale neonatal
screening, adult screening, full hearing diagnostic is disclosed.
The apparatus (100) contains a signal processor (1), integral ear
probe (150), and remote ear, and scalp probes (104) all packaged as
a single handheld battery operated device (100). The apparatus
(100) preferably performs a battery of tests, either independently
or combined: oto-acoustic measurements utilizing a novel digital
signal processing method for evoked oto-acoustic signal processing,
auditory brain stem response test, tympanometry, and
oto-reflectance. Algorithms for automatic test sequence, and
pass/refer indication for the tests are provided.
Inventors: |
Causevic; Elvir (Jefferson
County, MO), Causevic; Eldar (Jefferson County, MO) |
Assignee: |
Everest Biomedical Instruments
Co. (St. Louis, MO)
|
Family
ID: |
36126489 |
Appl.
No.: |
10/019,451 |
Filed: |
July 30, 2002 |
PCT
Filed: |
April 28, 2000 |
PCT No.: |
PCT/US00/11389 |
371(c)(1),(2),(4) Date: |
July 30, 2002 |
PCT
Pub. No.: |
WO00/65983 |
PCT
Pub. Date: |
November 09, 2000 |
Current U.S.
Class: |
600/561 |
Current CPC
Class: |
A61B
5/121 (20130101); A61B 5/7257 (20130101) |
Current International
Class: |
A61B 005/00 () |
Field of
Search: |
;600/559,561 ;73/585
;128/898 ;702/57 ;381/23.1,60 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
4234782 |
|
Apr 1994 |
|
DE |
|
9843566 |
|
Oct 1998 |
|
WO |
|
Primary Examiner: Hindenburg; Max F.
Assistant Examiner: Szmal; Brian
Attorney, Agent or Firm: Polster, Lieder, Woodruff &
Lucchesi, L.C.
Parent Case Text
This application claims of U.S. Provisional Ser. No. 60/131,542,
filed Apr. 29, 1999.
Claims
What is claimed is:
1. An auditory screening device, comprising: a portable hand-held
enclosure; a signal processor housed by said enclosure, said signal
processor configured with a computer program operated on command by
a user to produce one or more auditory tests and associated
stimulus signals selected from a group comprising otoacoustic
auditory emission test procedures, auditory brainstem response test
procedures, tympanometry, and otoreflectance for a test subject; a
memory module housed by said hand-held enclosure, said memory
module operatively connected to said signal processor and
configured to maintain at least one test subject record; a display
device mounted to said enclosure, said display device being
operatively connected to said signal processor for displaying
results of a selected auditory test in real time; a probe
connection point on said enclosure, said probe connection point
being operatively connected to said signal processor; a power
supply; and wherein said signal processor is configured to perform
a time domain sum and average over time for detecting otoacoustic
auditory emission signals using an offset frame overlap method.
2. An auditory screening device, comprising: a portable hand-held
enclosure; a signal processor housed by said enclosure, said signal
processor having a computer program operated on command by a user,
said program configured to produce auditory tests selected from a
group comprising otoacoustic emission test procedures, auditory
brainstem response test procedures, tympanometry, otoreflectance,
and combinations thereof for a test subject; a display device
mounted to said enclosure, said display device being operatively
connected to said signal processor, said display device displaying
the results of the selected test in real time; a probe connection
point on said enclosure, said probe connection point being
operatively connected to said signal processor; and a power supply
for operating the signal processor; wherein said signal processor
is configured to perform a time domain sum and average over time
for otoacoustic emission test signal detection, using a frame
overlap method; and wherein said auditory screening device further
comprises a memory subsystem that includes provisions for patient
data.
3. The device of claim 2 wherein an auditory brainstem test signal
is determined by digital signal processing and counting zero
crossings of correlated internally generated sinusoids.
4. A method of conducting an otoacoustic auditory emission audio
test, comprising the steps of: inserting a probe in a patient's
ear, said probe including a speaker and a microphone; connecting
said probe to a hand-held device; generating an auditory signal in
said hand-held device, detecting incoming auditory signals
generated in said ear via said microphone; converting said incoming
auditory signals to digital signal data; storing said incoming
digital signal data in a new frame buffer; sizing said new frame
buffer to be an integer number of samples of two primary tones at
frequencies f.sub.1 and f.sub.2 and an integer number of samples of
a tone produced by said ear at frequency f.sub.dp ; passing digital
signal data from a single frame to a discrete Fourier transform
process to calculate a frequency specific magnitude and phase
content of said incoming auditory signal signal; comparing said
calculated magnitude and phase to a table to determine whether to
reject the digital signal data, to discard the digital signal data
but update a noise table; or to save the digital signal data;
collecting said digital signal data until a predetermined number of
frames have been saved; averaging said digital signal data over a
predetermined number of sequential frames, wherein data from
sequentially preceding frames is slid by a predetermined number of
data points prior to said averaging; converting said averaged data
to a frequency domain; and displaying said averaged frequency
domain data to the user in a hand-held device in real time.
5. The method of claim 4 further including the step of saving the
digital signal data internally in said hand-held device.
6. The method of claim 5 further including the step of sending to
the user an indication of the subject passing or failing the
test.
7. The method of claim 4 further including the step of transferring
said digital signal data from said hand-held device to an external
unit.
8. An auditory screening device comprising: a hand-held enclosure;
a signal processor within said enclosure; a memory module within
said enclosure operatively connected to said signal processor; a
display screen mounted to said enclosure, said display screen being
operatively connected to said signal processor; a computer program
at least partial contained in said signal processor, said computer
program being accessible by a user to perform an otoacoustic
emission test and an auditory brainstem response test for a test
subject, said memory module maintaining a plurality of test subject
records for display on said display screen; and wherein the
otoacoustic auditory emission information is recorded by frames,
and information from a preceding frame is used in connection with
information of a succeeding frame to reduce the signal to noise
level in the received signals.
9. The device of claim 8 wherein the amount of information employed
with a succeeding frame is obtained from the formula: ##EQU1##
where M equals overlap number, f.sub.n equals frame number, f.sub.s
equals frame size and f.sub.dd equals frame data cycle length.
10. The device of claim 9 wherein said computer program further
includes tympanometry test procedures conducted independently or in
conjunction with otoacoustic auditory emission and auditory
brainstem response tests.
11. The device of claim 10 wherein the computer program determines
data information for the brainstem response test by counting zero
crossings of a sinusoid.
12. A method of conducting an auditory test in which a reduced
noise ratio is obtained by: receiving auditory signal information
in frames; making a determination to accept a frame, reject a frame
and update a noise average, or to discard a frame based upon at
least one predefined parameter; and averaging data in a current
accepted frame with data from at least one previous accepted frame,
wherein said data from said at least one previous accepted frame is
slid by a predetermined number of data points.
13. A method of conducting an otoacoustic auditory emission test in
which reduced noise ratio is obtained by: receiving otoacoustic
auditory emission signal information in frames; overlapping
information from a proceeding frame for use in connection with
information from a succeeding frame; making a determination to
accept the data, to reject the data but update a noise average, or
to discard the data based upon predefined parameters; wherein an
overlap is determined from the formula: ##EQU2## where M equals
overlap number, f.sub.n equals frame number, f.sub.s equals frame
size and f.sub.dd equals frame data cycle length.
14. The method of claim 13 further including the step of conducting
an auditory brainstem response test for a test subject.
15. The method of claim 14 wherein data for the auditory brainstem
response test is obtained by counting zero crossings of an
internally generated, correlated sinusoid.
16. An auditory screening device, comprising: a portable hand-held
enclosure; a signal processor housed by said enclosure; at least
one input/output interface housed by said enclosure and operatively
coupled to said signal processor; a memory module housed by said
enclosure, said memory module operatively connected to said signal
processor and configured to maintain at least one test subject
record; wherein said signal processor is configured to transmit and
receive signals through said at least one input/output interface to
conduct one or more auditory test procedures selected from a group
comprising otoacoustic emission test procedures, otoreflectance
test procedures, auditory brainstem response test procedures,
tympanometry test procedures on a test subject; and wherein said
signal processor is configured to process otoacoustic emission
signals received through said input/output interface using an
offset frame overlap method to reduce uncorrelated noise present in
results associated with said otoacoustic emissions test
procedure.
17. The auditory screening device of claim 16 further including: a
display screen mounted to said enclosure, said display screen being
operatively connected to said signal processor; and wherein said
signal processor is further configured to display results
associated with a selected test procedure on said display
screen.
18. The auditory screening device of claim 16 wherein said at least
one input/output interface is an otoacoustic emission interface,
said otoacoustic emission interface including at least one sound
transducer configured to present a variety of acoustic signals to a
test subject ear, and a microphone configured to receive response
acoustic signals from said test subject ear.
19. The auditory screening device of claim 18 wherein said
otoacoustic emission interface is further configured for
otoreflectance measurements of a test subject middle ear
condition.
20. The auditory screening device of claim 18 wherein said signal
processor is further configured with an otoacoustic auditory
emission simulator program, whereby said signal processor is
configured to generate simulated f.sub.dp tones in response to
tones generated by said sound transducer.
21. The auditory screening device of claim 16 wherein said at least
one input/output interface is an auditory brainstem interface, said
auditory brainstem interface including at least one sound
transducer configured to present an auditory stimulus to a test
subject ear, and at least one electrode configured to receive
response bioelectrical signals from said test subject.
22. The auditory screening device of claim 16 wherein said at least
one input/output interface is a tympanometry interface, said
tympanometry interface including at least one electronic control
channel, a pump operatively coupled to said electronic control
channel for altering a pressure level in a test subject ear, and a
pressure sensor configured to measure said pressure level in said
test subject ear.
23. The auditory screening device of claim 16 wherein said signal
processor is further configured, for each auditory test procedure,
to transmit at least one stimulus signal though said input/output
interface.
24. The auditory screening device of claim 16 further including a
display device mounted to said enclosure, said display device being
operatively connected to said signal processor, said display device
displaying the results of said one or more selected auditory test
procedures.
Description
TECHNICAL FIELD
This invention relates to the field of auditory measurement devices
and associated screening methods. In particular, the invention
relates to a hand-held auditory measurement device, which has
features beneficial to all neonatal screening programs. While the
invention is described with particular emphasis to its auditory
screening application, those skilled in the art will recognize the
wider applicability of the inventive principles disclosed
hereinafter.
BACKGROUND ART
Universal neonatal auditory screening programs have expanded
greatly because of improved auditory measurement capability,
improved rehabilitation strategies, increased awareness of the
dramatic benefits of early intervention for hearing impaired babies
and changes in governmental policies. Current neonatal auditory
screening approaches, however, do not account adequately for the
many different types and degrees of auditory abnormalities that are
encountered with present screening approaches. Because of this,
individual screening tests based on a single measurement can be
influenced negatively by interaction among various independent
auditory abnormalities. Current screening approaches have not
considered adequately the entire screening program including (i)
physical characteristics of the measurement device i.e.,
portability, physical size and ease of use, (ii) operational
characteristics of the device i.e., battery life, amount of record
storage, required operating training, etc. and/or (iii) program
logistics i.e., retesting mechanisms, referral mechanisms record
processing, patient tracking, report writing, and other practical
aspects. These factors can interact negatively to increase the
total cost of an auditory screening program including the primary
economic cost of screening, testing, the secondary economic cost of
additional testing, and non-economic costs such as parental anxiety
incurred when provided with incorrect information.
These costs, both actual and human, can be reduced by reducing the
cost per test, reducing the false positive rate, and resolving
false positive screening results at the bedside prior to hospital,
discharge. The cost per screening can be reduced with a dedicated
device optimized for screening in any location and enhanced to
allow effective operation by minimally trained personnel. The
performance characteristic of the device of our invention includes
reduced measurement time, the ability to operate and configure
without an external computer, the ability to integrate and
interpret all test results, the ability to store large number of
test results, long battery life, and bi-directional wireless
transfer of data to and from external devices.
We have found false positive results can be reduced in two ways.
First, the initial screening test performance can be improved with
enhanced signal processing, more efficient test parameters, and by
combining different types of tests. Second, false positive rates
also can be reduced by providing a mechanism for resolving an
initial screening test failure at the bedside at the time of the
initial screening. This capability is provided through the
availability of an automated screening auditory brainstem response
(ABR) test capability provided by the same device. Secondly,
operational processes of a screening program can be improved
through the use of several onboard computer based expert systems.
These computer based expert systems provide improved automatic
interpretation of single test results, automatic interpretation of
multiple test results, and improved referral processes through the
matching of local referral sources with various test outcomes, such
as a referral to a specific type of follow-up, whether it be a
pediatrician, audiologist, otolaryngologist, or a nurse. The device
disclosed hereinafter integrates in a single, hand-held device, a
single stimulus transducer, a single processor and a single
software application for otoacoustic emission (OAE). ABR testing,
tympanometry and otoreflectance, as well as OAE simulator.
An auditory abnormality is not a single, clearly defined entity
with a single cause, a single referral source and a single
intervention strategy. The peripheral auditory system has three
separate divisions, the external ear, the middle ear, and the
sensorineural portion consisting of the inner ear or cochlea and
the eight cranial nerve. Abnormalities can and do exist
independently in all three divisions and these individual
abnormalities require different intervention and treatment. Prior
art physical and operational characteristics of devices and their
influences on program logistics can interact negatively to increase
the total cost of an auditory screening program. The primary
economic cost is the cost of each screening test though this is not
the only economic cost. A screening test failure is called a
"refer" and usually is resolved with an expensive full diagnostic
test scheduled several weeks after hospital discharge, resulting in
significant economic cost. A substantial portion of these costs is
unnecessary if the screening false positive rate is high. Non
economic costs include parental anxiety for false positive
screening results, unfavorable professional perception of program
effectiveness for programs with high false positive rates and even
inappropriate professional intervention because of misleading
screening results.
The intervention of multiple measurements into a single hand-held
instrument allows for very important new functionality not
available with existing neonatal auditory screening devices. This
functionality includes (1) detection of common external and middle
ear abnormalities; (2) the detection of less common sensorineural
hearing loss associated with outer hair cell abnormalities, and (3)
the detection of even less common sensorineural hearing loss
associated with inner hair cell or auditory nerve abnormality.
Moreover, the device disclosed hereinafter has the potential to
improve the accuracy and reliability of OAE measurements, to allow
for optimal interpretation of both the OAE and ABR results, and to
improve the referral process.
Attempts have been made in the past to provide the capabilities
provided by the present invention. In particular. U.S. Pat. Nos.
5,601,091 ('091) and 5,916,174 ('174) disclose audio screening
apparatus which purport to provide a hand-held portable screening
device. However, the screening device disclosed in those patents is
used in conjunction with a conventional computer, and requires a
docking station for full applicational use. In no way does the
disclosure of either patent provide a hand-held device that can be
used independently of any other computer. That is to say, the
invention disclosed hereinafter provides a device of significantly
reduced size i.e. hand-held, which is capable of providing OAE and
ABR testing, as well as tympanometry otoreflectance, and OAE
simulator. It can be operated in a stand-alone mode, independently
of any other computer connection, if desired. The device includes a
patient database, with names, and full graphic display capability.
The device also preferably is provided with a wireless infrared and
an RS 232 connection port to provide output directly to printers or
to a larger database where such is required.
The '174 and '091 patents also operate on a linear averaging method
to remove background noise. While such method works well for its
intended purposes, use of a linear averaging method is time
consuming. Consequently, we developed a frame overlap method for
rejecting noise and improving signal reliability in a device which
measures, in the embodiment illustrated, 71/4".times.3
3/4".times.11/2".
SUMMARY OF INVENTION
One of the objects of this invention is to provide a reduced size
hand-held device for auditory screening which provides OAE, ABR,
tympanometry, otoreflectance and OAE simulator operation.
Another object of this invention is to provide an audio screening
device, which is hand-held and operates in a fully stand-alone
mode, operating independently of any other computer connection.
Another object of this invention is to provide a hand-held device
that provides a patient database on the device.
Another objection of this invention is to provide a hand-held audio
screening apparatus that provides for full graphic display on the
device itself.
Another object of this invention is to provide a device that
increases noise rejection and reduces processing time through the
use of frame overlapping techniques.
A further object of this invention is to provide a device with ABR
testing that automates electrode impedance checking prior to
test.
Another object of this invention is to provide a device which is
low in cost, and which can be adapted to provide a wide ranging of
auditory screening applications.
In accordance with this invention, generally stated, an effective
auditory screening method and device are provided. The integration
of an OAE screening device and ABR screening device into a single,
hand-held instrument enables a user to detect less common
sensorineural hearing loss associated with outer hair cell
abnormalities and the detection of less common sensor hearing loss
associated with inner hair cell abnormalities. In the preferred
embodiment, the device includes a portable hand-held enclosure
containing a digital signal processor. The processor has a computer
program associated with it, capable of conducting both otoacoustic
emission test procedures and auditory brainstem response test
procedures for a test subject. A display device is mounted to the
enclosure, and displays patient information, test setup procedure,
and test results including graphing of test results. The enclosure
includes a connection point for a probe, the connection point being
operatively connected to the signal processor. The device also
includes an onboard power supply, making the device completely self
contained.
A method of testing OAE response in a test subject is provided
which utilize a unique method of noise reduction to provide
acceptable data even in high level ambient noise conditions of the
test subject's environment.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, FIG. 1 is a top plan view of one illustrative
embodiment of audio screen device of the present invention.
FIG. 2 is a view in end elevation;
FIG. 3 is a view in end elevation of the end opposite to that shown
in FIG. 2
FIG. 4 is a block diagrammatic view of the device shown in FIG.
1;
FIGS. 5 and 6 are block diagrammatic views of the algorithm
employed with the device of FIG. 1 in connection with ABR
testing;
FIG. 7 is a diagrammatic view of frame sliding implemented by the
algorithm of FIG. 4; and
FIG. 8 is a block diagrammatic view of the algorithm implemented
with respect to OAE testing to improve the signal to noise ratio
employed with the device of FIG. 1.
BEST MODE FOR CARRYING OUT THE INVENTION
The following detailed description illustrates the invention by way
of example and not by way of limitation. This description will
clearly enable one skilled in the art to make and use the
invention, and describes several embodiments, adaptations,
variations, alternatives and uses of the invention, including what
we presently believe is the best mode for carrying out the
invention. It will nevertheless be understood that no limitation in
the scope of the invention is thereby intended, and that
alterations and further modifications of the illustrative devices
is contemplated, including but not limited to further applications
of the principles of the invention illustrated herein as would
normally occur to one skilled in the art to which this invention
relates.
Referring now to FIGS. 1-3, reference numeral 100 illustrates one
embodiment of the audio screening device of the present invention.
The screening device 100 includes an enclosure 102, which in the
preferred embodiment, and for purposes of illustration and not for
limitation, measures 71/4" long by 33/4" wide by 11/2" deep. It is
important to note that the device 100 can be carried by the user
without compromise, and truly represents a portable hand-held
device having full functionality as described below. The device 100
includes a keyboard 5, an LCD display 4, an LED pass/refer
indicator 7, and an LED AC charging indicator 17. Again, by way of
illustration and not by limitation, it should be noted that the
screen 4 measures, in the preferred embodiment, approximately 2" by
33/8". The measurement is not necessarily important, except to show
that the LCD display is fully functional for a user, and the unit
can operate independently of any other computer system. In the
embodiment illustrated, the enclosure 102 also houses an infrared
port 18, a compatible RS-232 port 18a, a probe connection 90 for an
ear probe 150, and an interface 103 for a plurality of electrodes
104. The electrodes 104 are shown attached to a conventional
carrier 151.
Ear probe 150 is conventional and is not described in detail.
Suitable probes are commercially available from Etymotic Research,
Part No. ER-10C, for example.
A novel feature of this invention is the provision of an OAE
simulator ear probe interface 160. The simulator function permits a
user to test the integrity of the entire OAE test system, by
providing active feedback and simulation of a test subject's
ear.
Referring now to FIG. 4, a block diagram view of the device 100 is
shown and described. The device 100 contains OAE, ABR and OAE
simulator capabilities in a single, hand-held package. Preferably,
the system shown in FIG. 4 is manufactured on a single printed
circuit board, with mixed signal design for both analog and digital
operation. The device preferably is low powered, and generally
operates at 3.3 volts, except for the LCD 4 and some low power
portions of the analog circuitry employed with the device 100.
A digital signal processor 1 is the control for the device 100. In
the preferred embodiment illustrated, the processor 1 is a Motorola
chip DSP 56303. All signal processing functions described
hereinafter are performed by the processor 1, as well as the
control of all input and output functions of the device 100. In
addition, the graphic functions, user interface, patient data
storage functions and other device functionality are controlled by
the processor 1. In conventional design logic, the digital signal
processor 1 is used for signal processing, and a separate micro
controller is used for device control. We have been able to
eliminate the separate microprocessor, resulting in substantial
savings in space, cost and power consumption.
A memory subsystem 2 is operatively connected to the processor 1.
The memory subsystem 2 includes a random access memory 2a for
storing intermediate results and holding temporary variably an a
flash memory 2b for storing non-volatile, electrically programmable
variables, patient data and configuration information. In the
embodiment illustrated, the flash memory 2b is substantially
oversized, enable the device 100 to accommodate as many as 300 full
patient records, as well as multiple configurations files.
A memory mapped input/output device 3 is operatively connected to
the memory subsystem 2 and to the digital signal processor 1. The
memory mapped input/output 3 in turn is operatively connected to
the LCD display 4, the keyboard 5, the pass/referral LED indicator
7 and a real time clock 6.
The LCD display 4 is the largest non-custom LCD available. While
custom LCD displays can be obtained, they add prohibitive cost to
the product. The LCD display 4 provides the user with 128.times.256
pixels of graphics. That display is sufficient to present full
waveforms of audiometric tests conducted by the device 100. The
keyboard 5 preferably is a membrane switch keyboard, which
incorporates only the minimum keys necessary for operation of the
device 100. All keys are programmable, except for the on/off key
105.
A real time clock 6 is operatively connected to the processor 1
through the memory mapped device 3. The clock 6 enables the
processor 1 to provide a time stamp for each patient and test
performed, as well as providing time signals for internal operation
of the device 100.
The LED pass/refer diode 7 is used to convey test results to
non-trained users, namely a nurse as opposed to an audiologist or
otolaryngologist. Use of the LED 7 avoids confusion or
misinterpretation of the LCD graphics display 4, and allows use of
the device 100 in low light areas, where the LCD display 4 may be
difficult to interpret.
The plurality of analog to digital/digital to analog coder/decoders
8 (codecs 8) is operatively connected to the signal processor 1. As
will be appreciated by those skilled in the art, the codecs 8 are
special integrated circuit chips that perform analog to digital and
digital to analog conversion. The codecs 8 are operatively
connected to the signal processor 1 along a dedicated serial link
indicated by the reference numeral 107. The codecs 8 in turn are
operatively associated with a plurality of input/output devices,
which provide the functionality of the device 100 under control of
the processor 1.
An otoacoustic emission interface 9 is operatively connected to the
signal processor 1 through the associated codecs 8. The interface 9
preferably is a low noise, differential analog circuit with high
common mode noise rejection. The interface 9 is intended to drive
two sound transducers inserted in the ear canal which produce a
variety of signals, from pure tones at various frequencies to
chirps, clicks, sine waveforms etc. The otoacoustic emission
interface 9 can present tones at all standard audiometric
frequencies and sound pressure levels. The device employed with the
interface 9 includes a microphone, also inserted in the ear canal,
which collects signals coming back from the ear, and provides
sufficient linear amplification to present the signals to the
codecs 8. In various embodiments of this invention, the interface 9
also can be used for otoreflectance measurements for assessing some
middle ear conditions.
The ARB interface 10 consists of a plurality of analog signal
processing chips, not shown individually, which filter and amplify
the signals connected from the scalp of a subject via electrode
wires 104. In this mode of operation, the ear is presented with a
repeated auditory stimulus, which causes firing of the eighth
nerve, and the associated nerve, pass Into the brainstem. As those
firings occur, electrical potentials are generated all the way to
the scalp, and there they are detected by the electrodes 104. An
additional function of the interface 10 is to provide automated
impedance check of the placement of electrodes. Once the electrodes
are in place, a small current is, injected through the electrodes
into the scalp of the subject, and the impedance between electrodes
is measured. Impedance can be varied by placement of the
electrodes. Once the impedance is within a predetermined range for
operation, ABR signal connection can begin. It is important to note
that impedance checking can be accomplished without unplugging the
electrodes. That is to say checking is automatic. As later
described in greater detail, the measured ABR response is based on
the detection of a peak in the waveform in a point approximately up
to 15 milliseconds after a sound click, depending upon gestational
age or patient age. The actual latency of this peak is then
compared to the latency of this peak in normal hearing neonates or
adults.
The otoacoustic emission simulator interface 11 is used to check
the integrity of the OAE system. It includes a transducer or
speaker and a microphone. The microphone collects the signals
presented by the OAE probe, presents them to the codecs 8 and
processor 1 for signal processing, and then the speaker presents
the corresponding tone at the correct frequency and amplitude back
to the original OAE probe thus providing an active, calibrated test
cavity.
Our invention optionally may include a tympanometry interface 11a
in place of the interface 11. The tympanometry interface 11a
comprises an electronic output channel to drive a miniature pump,
not shown, which can produce pressure or a vacuum in the ear canal
of a test subject. A corresponding pressure sensor is used to
measure this pressure, and the signal from the pressure sensor is
fed into an analog input of the codecs 8. The signal can be used as
an independent feature, and the device will show full graphics
output on the LCD 4 in real time. In the alternative, this test may
be used in combination with the OAE or ABR test to compensate for
middle ear conditions.
A mode configuration system 12, a reset watchdog system 13, a
crystal clock 14, a power supply 15 and a battery charger 16 all
are also positioned within the enclosure 102 and operatively
connected to the processor 1. While each of these blocks is
required for operation of the device 102, they are standard in
nature and are not described in detail.
The processor 1 has an input output channel 18, which are
preferably an infrared connection and an isolated RS-232 interface.
The device 100 can communicate with any infrared compatible or
RS-232 compatible personal computer, printer, or other digital
device for data transmission. Data transmission may include patient
information, configuration data for the signal processor 1, or
software program updates.
A buzzer 19 also is provided. The buzzer 19 provides an audio
feedback to the user for keyboard actions and audio indication for
error conditions.
A serial port 20 also is operative connected to the processor 1.
The serial port 20 is utilized to provide direct programming of the
processor 1 from a personal computer, for example, and is intended
for use only for initial software download and major software
program upgrades of the processor 1.
A distortion product otoacoustic emission (DPOAE) is a tone
generated by a normal ear in response to the application of two
external tones. When two tones, f.sub.1 and f.sub.2 are applied to
an ear, the normal non-linear outer hair cells generate a third
tone f.sub.dp, which is called a distortion product. F.sub.dp then
propagates from the outer hair cells back to the ear canal where it
is emitted. The level of the DPOAE can be used as a measure of
outer hair cell function. If the outer hair cell system is absent
or otherwise not functioning properly, the non-linearity will be
absent or reduced and the f.sub.dp will either not be generated or
generated at a lower than expected level.
The measured DPOAE is highly dependent upon the specific tones that
invoke it. The frequencies of f.sub.1 and f.sub.2, and their
respective levels in the ear canal, L1 and L2 must be controlled
precisely. Under known signal conditions, the largest distortion
product is generated at a very specific frequency (f.sub.dp =2
f.sub.1 -f.sub.2), and level L.sub.dp. Comparison of the level of
L.sub.dp with known values from individuals with normal outer hair
cell systems forms the basis of the decision of whether the patient
either passed the screening (pass/refer LED 7) or requires a
referral for a more complete diagnostic testing.
Signals other than pure tones can be presented to the ear, which
will also evoke a response from the ear, such as clicks, chirps,
etc. DPOAE is used to as an example, the other stimuli would be
processed the same way.
The processor 1 utilizes a unique method of detecting signals for
the OAE test. While the method is a time domain sum and average
operation, the key concept is to reuse data from adjacent frames to
average with the current frame. This method is described for the
purpose of this specification as "sliding". The limit to the size
of the overlap is the auto correlation of original data. The method
works on the assumption that the data within the overlap frames is
different, and that the noise is uncorrelated. It is key to keep
the frame size an integer number (one or more) of the original data
cycles.
The important difference between the method of the present
invention and linear averaging is that the overlapping number M
(sum operation) equals ((frame number divided by (frame size minus
1)) times (frame size divided by (frame data cycle length plus 1)))
which is larger than the received data frame number by a factor by
which the previous frame is slid. Therefore, the expected
performance of this method is better than standard linear
averaging. In this method, the frame size divided by frame data
cycle length must be an integer. The method is shown
diagrammatically in FIG. 5 and FIG. 6.
The processor 1 algorithm is implemented and explained with
reference to FIG. 7 and FIG. 8. As there shown, the processor 1
sends an output through, the digital analog converter portion of
the codecs 8 through the OAE interface 9 to the ear probe, utilized
in conjunction with the device 100. The ear probe includes a
microphone which returns signals through the interface 9 and the
codecs 8 to a new frame buffer 111 in the processor 1. The size of
the new frame buffer 111 is calculated to be an integer number of
samples of the two primary tones at frequencies f1 and f2, and
also, an integer number of samples of the otoacoustic tone produced
by the ear at f.sub.dp. This is a critical step to assure quality
of subsequent signal processing, by avoiding windowing techniques,
which can introduce substantial artifacts. Tables of numbers for
each standard frequency employed in the device 100 and for other
frequencies in use or intended for use in the device 100 are
available, and are programmed into the algorithm once the user
selects the test frequencies. Should a combination of frequencies
by required for which no common integer number can be found to fit
in a practical size frame, the frame size is adjusted to f.sub.dp
and the frame is windowed prior to Fourier Transformation, but this
method is used only in extreme cases since in normal operation, the
required frequencies are available.
The data from the single frame is passed to a point Discrete
Fourier Transform 112 (DFT) block which calculates the signal's
magnitude and phase content, but only at frequencies of interest,
including f.sub.1, f.sub.2, f.sub.dp to determine a noise floor.
Windowing is induced prior to DFT to reduce edge effects, although
windowing induces energy at other bands. The block 112 is used only
for temporary calculations, and the windowed data is not reused
again. The output of block 112 is the magnitude and phase of
primary signals at f.sub.1 and f.sub.2 and the noise floor figure
of time at f.sub.dp. The output of block 112 forms an input to
frame rejection block 113 and to an on-line calibration calculation
block 114.
With the information on the magnitudes at various frequencies, a
noise calculation algorithm is employed at and around f.sub.dp to
determine the noise floor. The magnitude of the noise floor and
frequency content are used against a set of predetermined
conditions i.e. a comparison against an empirically derived table
contained in the processor 1, to determine the outcome of the
frame. That outcome has three distinct possibilities. First, if the
noise magnitude and frame content exceed a multi-threshold
condition at measured frequency bands, the new frame is rejected.
Second, if the noise magnitudes fall between a set of reject
thresholds and a set of accept thresholds, the data in the frame is
disregarded, but the noise information is kept to update the noise
level average.
Third, if the noise magnitudes are below the accept thresholds, the
frame is kept and passed on for further processing and the noise
magnitudes are averaged together with the noise average of the
previous frame. This information is used to update thresholds, such
that the system adapts to environmental conditions.
When the information about magnitudes of primary tones at f, and
f.sub.2, and the noise floor information at and around f.sub.dp, an
online calibration of the level of magnitudes takes place. Several
actions occur in the calibration block 114. First, if the noise
floor is large when no primary tones are present, the frequency of
the primaries is adjusted within predetermined limits. A new
f.sub.dp is calculated, and the noise content of frequency bins at
and around f.sub.dp is checked again. This process is repeated
until a stable, low noise floor is established. No primary tones
are played through the speaker through this process. Once the
primaries are presented, they are stepped up to the full output
amplitude, as programmed by the user and calibrated in the ear by
increasing the output of the codecs 8. No data collection from the
ear has taken place yet. At this time, if the level is not reached
in a user predetermined time, and at the rate of increase of the
primaries, the test is aborted due to lack of fit or the low
quality of fit of the probe in the ear canal. Once the proper fit
is achieved, and testing begins, data collection takes place.
During the entire process of data collection, the levels of tones
at f, and f.sub.2 are checked to ensure that they remain within
predetermined limits throughout the test. If they exceed those
limits, the output is adjusted up or down to compensate until a
maximum compensation limit is reached, at which time, the test is
aborted and the user is notified. Also, the magnitude at and around
f.sub.dp is continuously monitored to assure low noise floor, and
if necessary, the frequency of the primary tones are adjusted
on-line within predetermined limits to avoid the high external
noise region. The change in frequencies of the primaries is
minimal, and within the specified tolerances of the device 100, and
have been shown not to affect the magnitude of the tone within the
car at f.sub.dp.
The block 115 is a store/copy buffer. As a frame is collected in
new frame buffer 111, a copy of it is saved for processing of the
subsequent frames.
The buffer 115 receives frame data from new frame buffer 111. The
store and copy frame buffer 115 has a variable depth, depending the
number of frames averaged together. Buffer 115 provides an output
to a block 116 and a block 17. The block 116 operates with the
stored previous frames, which are slid by a predetermined amount
and the empty spaces padded with zeros for subsequent processing in
the averaging old and new frame block 117.
In block 117, the frames are averaged together to reduce the
uncorrelated noise present. Theoretically, the noise is reduced by
a factor of one over the square root of the number of averaged
frames. The frames are averaged in a linear fashion, sample by
sample and a new frame is created at the end of the averaging
operation. The advantage of this method is that the data is
essentially correlated against a slid copy of itself, slid far
enough away to avoid averaging the same information content. This
provides either a substantial reduction in uncorrelated noise
energy for the same amount of sampling time or a substantial
reduction in sampling time to obtain the equivalent noise reduction
when compared to standard linear averaging.
The minimum limit to the sliding of the data, and to the reuse of
old data frame is the autocorrelation function of the data in the
frame, which can be predetermined or calculated on-line. This
method is equivalent to taking much smaller frames and averaging
them together. However, for the purposes of the subsequent Fourier
Transformations and filtering taking place, the frame size is
required to be large (i.e., 960 samples at 48 kilohertz sampling
rate), to obtain several full cycles of each of the tones at f1, f2
and f.sub.dp. The problem with taking a large number of very small
frames is that the Fourier Transforms or other signal processing
methods require several cycles of data for proper operation. The
method of the present invention outperforms standard linear
averaging of large frames because of the reduction in time as well
as providing proper operation of the Fourier Transforms.
The block 118 obtains the averaged data from the block 117, and
collects it in a buffer that is used for subsequent processing and
signal statistics. The output of the block 118 is digitally
filtered in the block 119. The filter 119 removes any remaining
high or low frequency components not required for final data
presentation.
The averaged and filtered data is converted to frequency domain, in
the embodiment illustrated, by using a discrete Fourier Transform
in the block 120, and the data then is ready for presentation in
block 121. As will be appreciated by those skilled in the art,
other signal processing methods are available to convert data, and
those other methods are compatible with the device 100.
As indicated above, the device 100 enables the LCD 4 to present
information to a user graphically in real time on the device
itself, complemented with textual and numeric information about the
quality of the fit, amplitudes, frequency, noise floors and other
related information.
Operation of the device for ABR testing is shown in FIG. 5 and FIG.
6. In ABR testing, the magnitude of the fifth peak is the one that
is of primary interest, and the device 100 determines the magnitude
of the fifth peak by counting zero crossings, after substantial
filtering and digital preprocessing. As shown in FIG. 5 and FIG. 6,
the system proceeds to count zero crossings and stores an index of
an array element upon determination of a zero crossing. If
additional zero crossings are required, the procedure is, repeated
until the fifth peak is determined. Upon detection, the single
waveform is isolated, and the waveform peak is correlated to find
the maximum correlation sinusoid. Thereafter, the device 100
determines the time of occurrence of the fifth peak and that value
is checked against empirical data to obtain proper correlation.
Numerous variations, within the scope of the appended claims, will
be apparent to those skilled in the art in light of the foregoing
description and accompanying drawings. For example, the design of
the enclosure may vary in other embodiments of the invention.
Likewise, LCD display 4 may be replaced with other display devices.
As indicated in the specification, we use a discrete Fourier
Transform to obtain data for display. Other signal processing
methods are compatible with the broader aspects of the invention.
These variations are merely illustrative.
* * * * *